1. Field of the Invention
The present invention relates to a color image forming apparatus and a method of using the same, and more particularly to a color image forming apparatus for forming latent images for a plurality of color images on a latent image bearing body and transferring the color images on a record sheet at a time, and a method of using such a color image forming apparatus.
2. Discussion of the Related Art
An example of printers known as color image forming apparatuses is of the so-called transfer drum type. In this type of printer, a photoreceptor drum rotating plural times is provided. Through the respective rotating cycles of the photoreceptor drum, toner images of the colors respectively corresponding to the rotating cycles are formed on the photoreceptor drum. A transfer drum is also provided, which rotates in contact with the photoreceptor drum and around which a record sheet is wound. The color toner images are transferred from the photoreceptor drum superposedly onto the record sheet, through the rotating cycles of the photoreceptor drum.
The printer of this type can form full-color images. However, even in forming images of two colors (e.g., black and red), which operation is frequently requested by users, it must rotate the photoreceptor drum plural times. Accordingly, it takes much time to form two-color images, like the case of forming full-color images.
There are proposals directed to the problem just mentioned (Japanese Patent Application Unexamined Publication Nos. Sho. 58-57139 and Sho. 60-247650). In the proposals, toner images for plural colors are formed on the photoreceptor drum, and are transferred from the photoreceptor drum onto a record sheet at once.
In the color image forming apparatuses proposed, a two- or three-color image can be formed by only one turn of the photoreceptor drum. The image forming time can indeed be reduced for those images. The apparatus, however, has the following shortcomings. First, it cannot form images of four or more colors. Second, the colors of a reproduced image is limited to the colors of the toners of the developing units. To perfectly satisfy the customer's desire for a particular color of a reproduced image, the toner in the developing unit must be replaced by the new one of the desired color.